Type of PEX for paver snow melt system?

davidd

Hello,

I will soon need to pull up some pavers in front of our house, in Minnesota, to fix a leak in the water service line between our well and our house. While I am at it, I want to install a hydronic snow melt system. I already have a boiler, hydronic air for heat, indirect water heater, etc. I'll have a closed loop, heat exchanger, glycol, etc.

My question is what type of PEX would you recommend for this application, and why?

A ) PEX-AL-PEX
B ) Oxygen barrier PEX
C ) Something else?

Thanks for your feedback,
David

kcopp

Is your boiler large enough?

Typically you need to figure 150 btu per ft2.

davidd

kcopp said:

Is your boiler large enough? Typically you need to figure 150 btu per ft2.

Boiler is about 170K BTU.  The paver area is relatively small.  Figure less than 50k BTU for the pavers.  The snow melt system will also only be used as needed, not continuously.

delcrossv

Oxygen barrier PEX , else you'll be continuously perfusing O2 into your heating system. Cast iron boilers don't like that at all.

https://canarsee.com/learning-center/differences-between-oxygen-barrier-and-non-barrier-pex-tubing#:~:text=Due%20to%20its%20oxygen%20barrier,Non%2DBarrier%20tubing%20would%20corrode.

Zman

PEX-A, either Uponer or Rahau would be my recommendation.

davidd

delcrossv said:

Oxygen barrier PEX , else you'll be continuously perfusing O2 into your heating system. Cast iron boilers don't like that at all. https://canarsee.com/learning-center/differences-between-oxygen-barrier-and-non-barrier-pex-tubing#:~:text=Due%20to%20its%20oxygen%20barrier,Non%2DBarrier%20tubing%20would%20corrode.

Thanks.  Pex-al-pex is an oxygen barrier pex.  I am wondering about pros and cons of pex-al-pex oxygen barrier vs non-pex-al-pex oxygen barrier, for this application.  The snow melt system will be on its own closed loop system, with a heat exchanger between that system and the hydronic air and indirect water heater system.

delcrossv

davidd said:

delcrossv said:

Oxygen barrier PEX , else you'll be continuously perfusing O2 into your heating system. Cast iron boilers don't like that at all.

https://canarsee.com/learning-center/differences-between-oxygen-barrier-and-non-barrier-pex-tubing#:~:text=Due%20to%20its%20oxygen%20barrier,Non%2DBarrier%20tubing%20would%20corrode.

Thanks.  Pex-al-pex is an oxygen barrier pex.  I am wondering about pros and cons of pex-al-pex oxygen barrier vs non-pex-al-pex oxygen barrier, for this application.  The snow melt system will be on its own closed loop system, with a heat exchanger between that system and the hydronic air and indirect water heater system.

Yep. PEX-AL-PEX would work as well.

davidd

Zman said:

PEX-A, either Uponer or Rahau would be my recommendation.

Thank you.  The Uponor oxygen barrier PEX is the hePEX?  Any particular reason for that vs PEX-AL-PEX?

delcrossv

Yes, it's hePEX.
If it were me, I'd consider Pex-Al-Pex as the barrier is internal to the tube rather than a coating on it and IIRC has less expansion. Either will work.

https://plasticpipe.org/BuildingConstruction/BuildingConstruction/PEX-AL-PEX.aspx

davidd

delcrossv said:

Yes, it's hePEX. If it were me, I'd consider Pex-Al-Pex as the barrier is internal to the tube rather than a coating on it and IIRC has less expansion. Either will work.

Thanks for the feedback.

That's what I keep going back and forth with in my head.  With the non-AL pex, I am wondering about movement, from expansion, and rubbing on the metal grid, as this will be in sand, not concrete.  I also don't have a good feel for whether non-AL, oxygen barrier pex will still allow enough oxygen in over time to mess with iron pumps, and chemistry of the fluid. 

With AL pex, I am wondering about having more problems with fittings and kinks when installing, and the tubing splitting if it freezes (I plan to have it run automatically, periodically, when cold enough, but sensors can fail and power can go out).

delcrossv

Not going to run glycol in that loop? As it is isolated on it's side of the HX, would make sense to.That should take care of the loop freezing. Either type satisfies the ASME standard for hydronic.

GroundUp

Pex-A is the easiest to work with and will also allow some flexibility with earth movement and if there is a glycol issue at some point down the road where freezing becomes a possibility. Pex-A will take that kind of abuse to some extent, PAP will split pretty easily.

davidd

delcrossv said:

Not going to run glycol in that loop? As it is isolated on it's side of the HX, would make sense to.That should take care of the loop freezing. Either type satisfies the ASME standard for hydronic.

It will have glycol.  But even that freezes after a certain point.  I can get soil temperatures for various locations and depths to use as a reference.  But what I don't know is how the different composition of materials will affect it, and I don't know how much the insulation will allow the area above it to get colder than usual.  In other words, if there was no insulation, the heat from the ground would be working against the air trying to cool the surface layers.  With insulation in place, and the system not running, I don't know whether the insulation slowing the heat migration from below it will allow the layers above it to get extra cold.

It probably isn't going to freeze with a 50/50 mix.  My memory says that is good down to about -15 degrees F.  I am guessing it would need to be a real cold spell for upper layer ground temps to get that cold.

What ratio do others use for Minnesota or neighboring states for snow melt applications?

GroundUp

50/50 means nothing without the beginning concentration percentage. If you go to Menards and buy Cryo-Tek -100 and mix that 50/50, you only have 27.5% concentration because it's 55% right from the bucket. Cryo-Tek AG is about 96% from the bucket so 50/50 would put you right where you want to be. I run all my snowmelt in MN at 47%.

davidd

GroundUp said:I 

50/50 means nothing without the beginning concentration percentage. If you go to Menards and buy Cryo-Tek -100 and mix that 50/50, you only have 27.5% concentration because it's 55% right from the bucket. Cryo-Tek AG is about 96% from the bucket so 50/50 would put you right where you want to be. I run all my snowmelt in MN at 47%.

I meant 50/50 end result.  Thanks for the real world MN info.  Any particular reason for picking that brand?  Not questioning it.  I haven't looked into brands to see if there are chemistry advantages and ones that are recommended more than others.

Have you done any snow melt under pavers?  If so, what layering do you have under them?

From your earlier comment, where you mentioned Pex-A, if you have done non-cement systems, do you attach it to a metal grid to limit movement?  Any problem with it rubbing on the metal and wearing through?

What temp do you run your snow melt systems at, and what type of response do you get out of them?  By that, I mean, how long to melt a given amount of snow?  5/8 or 3/4" pex?

I'd really rather not have to re-do pavers in the future, after this project, so that's why I'm pondering some of these variables.

Thanks again for the info.  I really appreciate it.  

GroundUp

@davidd I don't do the base or pavers themselves, but I have done snowmelt in a number of paver patios and driveways. I typically either run my tubing in Heat-Sheet foam with the nodules to hold the tubing, or just regular foam board with foam staples. I did use 1/4" welded mesh once on a job where the owner was an engineer and thought insulation was stupid because "the earth remains a constant 51 degrees and will help melt the snow", which obviously is not the case or we wouldn't have any snow to melt. I would never do that on purpose, for the reason you mentioned. Then the landscaper guy comes behind and does his thing. Some use sand, some use stone dust, some use crushed granite, I even saw someone use class 5 once. Each system is different and is based on the desired melting rate, but I'd say a typical paver system on stone dust comes out to that 120* SWT area. Slabs can run a little cooler, sand beds a little warmer. This obviously varies with outdoor temperature and fall rate, but most can melt a couple inches per hour with 120* SWT and a 20* outdoor temp assuming proper drainage. I did have one that runs at 170* on a very steep driveway in Minnetonka and the owner just lets it run all winter with a 60* surface temp to make sure there's never any accumulation.

davidd

GroundUp said:

@davidd I don't do the base or pavers themselves, but I have done snowmelt in a number of paver patios and driveways. I typically either run my tubing in Heat-Sheet foam with the nodules to hold the tubing, or just regular foam board with foam staples. I did use 1/4" welded mesh once on a job where the owner was an engineer and thought insulation was stupid because "the earth remains a constant 51 degrees and will help melt the snow", which obviously is not the case or we wouldn't have any snow to melt. I would never do that on purpose, for the reason you mentioned. Then the landscaper guy comes behind and does his thing. Some use sand, some use stone dust, some use crushed granite, I even saw someone use class 5 once. Each system is different and is based on the desired melting rate, but I'd say a typical paver system on stone dust comes out to that 120* SWT area. Slabs can run a little cooler, sand beds a little warmer. This obviously varies with outdoor temperature and fall rate, but most can melt a couple inches per hour with 120* SWT and a 20* outdoor temp assuming proper drainage. I did have one that runs at 170* on a very steep driveway in Minnetonka and the owner just lets it run all winter with a 60* surface temp to make sure there's never any accumulation.

That is great information.   Thanks for sharing your knowledge and experiences.  That heat sheet foam looks really interesting.  Do you feel there is any measurable difference in conduction of the heat out of the pex and into the sand between the heat sheet and having the pex stapled to foam?  The reason I ask is because I am wondering if the parts of the pex that have those knobs wrapped around them would reduce heat transfer, vs open (except on the very bottom) with the plastic staple approach.

You brought up drainage.  How do you typically see that done with a paver system, where the water will be soaking into the sand and hitting the foam insulation?  Do you poke holes in the insulation for drainage?  Or do you have a slope, so that it flows in that direction, and off the edge into something it can soak down into (or be carried away with a French drain type system)?

Running continuously, with a 60 degree surface temp!  Wow!  That's gotta boost the gas bill a bit.     

How many inches of sand is typical above the insulation?  And do you measure that from the top of the pex (for stapled) or top of the knobs (for heat sheet)?

My other challenge is I have a semi-circle of pavers that sits another several inches higher at the door.  And that is the area I'd like to de-ice the most.  I've been contemplating, below the semicircle, running closer spaced pex at the same level as the rest.  I could then use aluminum heat plates (like the type used in indoor, underfloor/staple up systems).  I could then bolt on some vertical aluminum pieces to act as fins to get the heat up into the sand closer to the bottom of the pavers in the semicircle.

Open to other ideas for how to approach the higher level semi-circle.

Thanks again!
David

hot_rod

Pex al pex is not such a friendly tube to use if you are a newbie?
Also if the entry is a very small area a short loop of 1/2 allows for 6” spacing and easy to use in odd shape spaces.

GroundUp

I've never gotten into the data collection side of this, but I do think there is a small amount of lost transfer due to the nodules in Heat-Sheet or Crete-Heat or those other types compared to stapling over foam. Measurable? Probably not. Most are simply sloped to some sort of surface drain, but I have seen a few where they placed drains at foam height and let it filter through the pavers. I don't have a good answer for what the ideal scenario is, as all my snowmelt at home is concrete and I would never have it any other way. Call it a bias, if you will. Sand typically ends up around 2" above the tubing or nodule, I'm guessing mostly for play but again that's not my bag of marbles so I can't say with any accuracy. I'm typically long gone before that part of the job gets done.

hot_rod

Tube at the bottom of a 4” slab will take around 7 degree SWT to get the same output as tube mid slab

With tube on 6x6 mesh you get a better chance of getting concrete around the tube, and the best transfer, The foam nubs tend to put a foam isolation piece around the tube

Ideally, take the time to fasten to mesh or rebar and elevate it on chairs for best performance.

On a small job like this it should not add much hassle factor

I did some testing on the nub panels to see what the bottom of the pour looks like, measured performance difference

PC7060

@hot_rod - have you considered a password manager? 

hot_rod

PC7060 said:

@hot_rod - have you considered a password manager? 

For my Swiss bank  accounts?

Derheatmeister

delcrossv said:

Oxygen barrier PEX , else you'll be continuously perfusing O2 into your heating system. Cast iron boilers don't like that at all.

https://canarsee.com/learning-center/differences-between-oxygen-barrier-and-non-barrier-pex-tubing#:~:text=Due%20to%20its%20oxygen%20barrier,Non%2DBarrier%20tubing%20would%20corrode.

Agree with the O2 Barrier....But... for various reasons would you not want to install a HX between the Cast iron boiler and the snowmelt ?

PC7060

hot_rod said:

PC7060 said:

@hot_rod - have you considered a password manager? 

For my Swiss bank  accounts?

Haha, nope, I noticed your screen shot had captured part of the screen show a file named “passwords”

hot_rod

PC7060 said:

hot_rod said:

PC7060 said:

@hot_rod - have you considered a password manager? 

For my Swiss bank  accounts?

Haha, nope, I noticed your screen shot had captured part of the screen show a file named “passwords”

Thanks for catching that!

davidd

hot_rod said:

Tube at the bottom of a 4” slab will take around 7 degree SWT to get the same output as tube mid slab With tube on 6x6 mesh you get a better chance of getting concrete around the tube, and the best transfer, The foam nubs tend to put a foam isolation piece around the tube Ideally, take the time to fasten to mesh or rebar and elevate it on chairs for best performance. On a small job like this it should not add much hassle factor I did some testing on the nub panels to see what the bottom of the pour looks like, measured performance difference

Thanks.  In this case, it will be about 2" of sand above it, rather than a slab.  I will take a look at the nub panel data.

davidd

hot_rod said:

Tube at the bottom of a 4” slab will take around 7 degree SWT to get the same output as tube mid slab With tube on 6x6 mesh you get a better chance of getting concrete around the tube, and the best transfer, The foam nubs tend to put a foam isolation piece around the tube Ideally, take the time to fasten to mesh or rebar and elevate it on chairs for best performance. On a small job like this it should not add much hassle factor I did some testing on the nub panels to see what the bottom of the pour looks like, measured performance difference

Did you happen to measure the difference of foam nubs vs grid when they were both at the same depth? 

hot_rod

davidd said:

hot_rod said:

Tube at the bottom of a 4” slab will take around 7 degree SWT to get the same output as tube mid slab

With tube on 6x6 mesh you get a better chance of getting concrete around the tube, and the best transfer, The foam nubs tend to put a foam isolation piece around the tube

Ideally, take the time to fasten to mesh or rebar and elevate it on chairs for best performance.

On a small job like this it should not add much hassle factor

I did some testing on the nub panels to see what the bottom of the pour looks like, measured performance difference

Did you happen to measure the difference of foam nubs vs grid when they were both at the same depth? 

No, just the Tube on the nubs and tube in the middle of a 4” pour.